How foodborne bacteria make people sick depends on a variety of factors, and better understanding of the infection process could lead to ways to stop such illnesses from occurring, according to Purdue University scientists.
In the first comprehensive study of the virulence of Listeria monocytogenes, researchers report that how well the bacteria attach to cells does not alone determine the degree of illness.
The factors that determine if a person becomes ill and the degree of illness include the levels at which the pathogen attaches to intestinal cells, penetrates cell walls and then moves into other organs, claim authors Arun Bhunia and Ziad Jaradat, both of the university's Department of Food Science. The paper is published in the June issue of Applied and Environmental Microbiology.
Listeria is one of the deadliest foodborne bacteria, with a fatality rate of 20 per cent, according to the Centers for Disease Control and Prevention (CDC). It sickens about 2,500 people annually in the United States.Listeria strains can enter the brain within 72 hours of when tainted food is eaten.
"I'm interested in understanding how the bacteria interacts with the intestinal cells," said Bhunia. "If you eat food that contains these bacteria, the first place they react with cells is in the intestinal track. If we understand the initial interaction of Listeria in the gut, we might be able to prevent the binding and, therefore, the infection."
Bhunia and his co-author studied 25 strains of Listeria, including some that specifically have caused outbreaks of human illness. In the past two decades, four types of Listeria monocytogenes have been responsible for 90 per cent of the outbreaks of the illness they cause, listeriosis, according to the CDC.
"This is the first comprehensive study in which this many strains of Listeria were tested for all three infection aspects - adhesion, invasion and translocation," Bhunia said. "We didn't find any direct relationship between adhesion and invasion; adhesion is needed but is not an indicator of infection."
The researchers are now studying individual proteins that may play a role in Listeria binding to cells. If they can identify those proteins, they may be able to use genetically modified versions to prevent the infection process. The US Department of Agriculture Agricultural Research Service and the Purdue Center for Food Safety and Engineering provided funding for this study.